There have been many problems associated with developing hard surface coatings that provide a beneficial layer with the desirable properties and which minimize the disadvantages, such as a limit to single use protection, insufficient coverage, roughness and/or flaking of coating during use, or in contrast, the inability to remove once applied (when a more temporary coating is desired), a limit on surfaces that can be modified, photoactive damage and degradation of the surface, and in the case of TiO2, the need to photoactivate the coating.
Current approaches to solving the coating problem use surfactants, film-forming polymer coatings, clay-containing-film-forming polymer coatings and photoactive inorganic metal oxide coatings. However, the substantivity of the film-forming polymers (e.g. alkoxylated silicones, poly(N-vinyl-2-pyrrolidones, poly(N-vinyl-imidazoles, diblock copolymers of poly(ethylene oxide) and poly(lactide)) is poor such that its wetting/sheeting effect is short-lived, with spotting/residue negatives returning within 1-2 rinses, exposures to the elements (e.g., rain, etc.), or conditions (e.g., water in a shower). Elevating the levels of polymers is not the solution to this problem. This is especially evident on automobile surfaces, residential windows, building exteriors, shower units and dishware where elevated levels of polymers result in unacceptable residue problem. In the case of clay-containing, film-forming polymer coatings, the nanoparticles are rheology agents for the formulations and do not themselves impart the benefit disclosed.
Additional background patents and patent publications, some of which disclose various uses of nanoparticles, include: U.S. Pat. Nos. 4,591,499 and 4,597,886; JP 04-353438; U.S. Pat. No. 5,429,867; JP 96053558; GB 2 303 373; U.S. Pat. No. 5,853,809; PCT WO 99/00457; WO 00/000554 A1; WO 01/27236; and WO 01/32820.